背景回顾：Differential regulation of stem cell activity in shoot meristems contributes to the wide variation in shoot architecture. In most Citrus species, a thorn meristem and a dormant axillary meristem co-localize at each leaf base, offset from each other in a spiral phyllotactic pattern. 

研究基础：We recently identified THORNIDENTITY1 (TI1) and THORN IDENTITY2 (TI2), encoding TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP) transcription factors, as necessary for the termination of meristem proliferation and concomitant thorn production in Citrus. 

提出问题：However, how the dormant axillary meristem at the same leaf axil maintains stem cell activity is still unknown.

主要研究：The phosphatidylethanolamine-binding protein (PEBP)-type transcription factors CENTRORADIALIS (CEN) and TERMINAL FLOWER1 (TFL1) maintain inflorescence meristem indeterminacy in many plant species by antagonizing floral meristem identity regulators. Here, we show that, in Citrus, Citrus CEN (CsCEN) maintains vegetative axillary meristem indeterminacy by antagonizing TI1.

结果1-CsCEN表达模式：CsCEN is expressed in the axillary meristem, but not in the thorn meristem. 

结果2-CsCEN功能：Disruption of CsCEN function results in termination of the stem cell activity and conversion of dormant axillary meristems into thorns, although ectopic overexpression of CsCEN represses TI1 expression and converts thorns into dormant buds, a phenotype similar to the ti1 mutant. 

结果3-CsCEN互作因子：We further show that CsCEN interacts with Citrus FLOWERING LOCUS D (CsFD) to repress TI1 expression. 

结果4-CsCEN与TI1/2：CsCEN activity depends on the function of TI1 and TI2, as mutations in TI1and TI2 rescue the cscen mutant phenotype. 

结论：We suggest that the antagonistic roles of CsCEN and TI1 define the pattern of axillary meristem determinacy, which shapes vegetative Citrus tree shoot architecture.

茎尖分生组织中干细胞活性的差异性调控作用于植物地上组织结构的广泛变异。在大多数柑橘物种中，一个刺（thorn）分生组织和一个休眠的腋分分生组织共定位于每一片叶的基部，并以螺旋状的叶序模式相互间隔。作者最近鉴定了编码TCP转录因子的TI1和TI2基因，是柑橘分生组织增殖停止及同时形成刺的必要基因。但是，位于同一叶腋中的休眠腋分生组织如何维持干细胞活性并不清楚。在大多数植物物种中，PEBP类转录因子CEN和TFL1通过拮抗调控花分生组织调控因子，维持花序分生组织的无限性。本文中，作者发现柑橘的CEN基因（CsCEN）通过拮抗TI1基因维持营养腋分生组织的无限生长。CsCEN在腋分生组织中表达，但是不在刺分生组织中表达。扰乱CsCEN的功能会导致干细胞活性的终止，并且腋分生组织会转化成刺分生组织，而异位过表达CsCEN基因会抑制TI1的表达，并将刺转变为休眠芽，类似于ti1突变体的表型。作者进一步发现CsCEN会与柑橘的CsFD互作，从而抑制TI1基因的表达。CsCEN的活性依赖于TI1和TI2基因的功能，TI1和TI2基因的突变能够拯救cscen突变体的表型。本文的研究揭示了柑橘CsCEN和TI1基因之间的拮抗作用，决定了腋分生组织的无限性模式，从而塑造了柑橘地上组织营养器官的结构。